This disclosure concerns orthopedic implants, including spinal implants such as intervertebral prostheses and intersomatic cages, for example. In particular, this disclosure is directed to devices and methods for removing fixation devices, such as anchors, pins, staples, screws, nails, etc., that have been used to affix an intervertebral implant to one or more adjacent spinal elements.
A healthy intervertebral disc is flexible enough to allow movement between a vertebra and another adjacent spinal column element, such as another vertebra, the coccyx, or the sacrum. This movement accommodates bending of the spine. Disease, degeneration, or injury of the tissues of a natural intervertebral disc often leads to intense pain and reduced spinal mobility. When disease, degeneration, or injury of the natural intervertebral disc has progressed to the point where non-operative care such as medication, injections, and/or physical therapy is ineffective, surgical intervention may be required.
A common procedure for treatment of diseased, degenerated, or injured intervertebral discs involves removal of the natural tissues of the disc and fusion of the adjacent vertebrae. Although fusion eliminates the mobility between the adjacent vertebrae, often it is the preferred method of treatment of disc degeneration or injury.
Intervertebral disc prostheses have been developed to treat diseased, degenerated, or injured intervertebral discs and still provide a relatively normal range of movement to the adjacent vertebra, resulting in a more normal distribution of stresses and movements along the various segments of the spine. Intervertebral disc prostheses typically are configured to restore normal disc height, and can decrease surgical morbidity and complications from postoperative immobilization instrumentation that may be present in fusion procedures.
One problem in this field concerns the stability of spinal implants in the disc space once they have been implanted. For example, there is a risk that the implant will shift in the intervertebral space due to forces imposed when the patient moves, even when the implant is provided with notches or teeth on its vertebral contact surfaces. Therefore, it is often necessary to affix the spinal implant to the adjacent vertebrae during implantation. A number of solutions are known to affix the spinal implant to the adjacent vertebrae using a bone anchoring device, such as an anchor, pin, nail, screw, staple, and other mechanical fixation structures. International Application No. PCT/IB2009/008048 filed Dec. 31, 2009, by the assignee of the present application describes various particularly advantageous fixation devices, instruments, and methods.
Access to the intervertebral spaces often is particularly delicate due to the dimensions involved and the presence of blood vessels and nerves in the approach to the intervertebral space. Bone anchoring devices should have sufficient size, strength, and positioning to ensure good fixation, but preferably the configuration of the anchoring devices, installation tools, and fixation methods allows fixation of the implant without endangering the surrounding blood vessels and nerves. International Application No. PCT/IB2009/008048, for example, describes various advantageous devices, instruments, and methods that reduce the space required in the approach to the intervertebral location compared to conventional devices and methods.
In an ideal outcome, the placement an intervertebral implant will be permanent, and withdrawal of the implant or modification of its position never will be needed. In practice, though, circumstance can arise which indicate that an intervertebral implant should be removed or reposition following the initial fixation to the adjacent vertebral structures. This disclosure describes various structures and steps that may be useful for removing or repositioning an implant after its initial fixation.